#define _CRT_SECURE_NO_WARNINGS 1

int main()
{
    int flag = 1;
    int n = 0;
    scanf("%d", &n);
    int sum = 0;
    for (int i = 1; i <= n; i++)
    {
        sum += flag * i;
        flag = -flag;
    }
    printf("%d\n", sum);

    return 0;
}